package org.apache.solr.util;

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.util.concurrent.Semaphore;

final public class AdjustableSemaphore {

	private final ResizeableSemaphore semaphore;

	private int maxPermits = 0;

	public AdjustableSemaphore(int size) {
		semaphore = new ResizeableSemaphore(size);
	}

	public synchronized void setMaxPermits(int newMax) {
		if (newMax < 1) {
			throw new IllegalArgumentException(
					"Semaphore size must be at least 1," + " was " + newMax);
		}

		int delta = newMax - this.maxPermits;

		if (delta == 0) {
			return;
		} else if (delta > 0) {
			this.semaphore.release(delta);
		} else {
			delta *= -1;
			this.semaphore.reducePermits(delta);
		}

		this.maxPermits = newMax;
	}

	public void release() {
		this.semaphore.release();
	}

	public void release(int numPermits) {
		this.semaphore.release(numPermits);
	}

	public void acquire() throws InterruptedException {
		this.semaphore.acquire();
	}

	public synchronized int getMaxPermits() {
		return maxPermits;
	}

	private static final class ResizeableSemaphore extends Semaphore {

		ResizeableSemaphore(int size) {
			super(size);
		}

		@Override
		protected void reducePermits(int reduction) {
			super.reducePermits(reduction);
		}
	}
}